README
Evan Dethier
2023-03-05
River mineral mining
Mapping and documenting the effects of mining for gold and precious minerals in streams and rivers across the world
What is river mineral mining?
River mineral mining is mining that occurs in and around rivers and streams. Such mining has a long history and many names, including “alluvial mining”, “placer mining” and “hydraulic mining”. We use the term “river mineral mining”, or sometimes just “river mining”, defined as any mining that has a direct surface water connection to a river. Sometimes, mining happens directly in rivers themselves. In other cases, miners excavate river banks, floodplains, and terraces.
Mining in rivers was key to the United States mining rushes of
the 19th century. High-powered jets of water were used to rapidly erode
river beds and banks, just as they are today in the tropics. This image
from California in the 1860s or 1870s shows hydraulic mining underway,
with excavation by high-powered jets of water. Image from the US Library
of Congress.1
How does river mining work?
In most cases, after excavation, miners process sediment to extract gold or other precious minerals. Often, miners do so by sending a slurry of water and sediment down a sluice. A sluice is a ramp or channel that has simple elements like riffles and settling boxes that use gravity to separate the precious minerals from the other sediment. Other separation methods exist as well, some larger and some smaller. But most of them use the same principle: gravity separating the targeted mineral from flowing water and sediment.
The excess sediment and water is often discharged directly into streams and rivers, either inadvertently during excavation or intentionally after separation. This input of sediment to rivers causes them to become cloudy or muddy. We measure such changes in muddiness as “suspended sediment concentration”, defined as the weight of sediment particles in a given volume of water. In many cases, chemical ore-processing aids, most commonly mercury, also flow into streams and rivers. Both the sediment itself and these chemical contaminants can cause serious environmental degradation in affected rivers, with negative consequences for fish and other flora and fauna.
Mining boom in the global tropics
River mineral mining in modern operations closely resemble past
operations. Here images from Peru show swaths of deforestation and
excavation in a mining region in Madre de Dios. Photos were taken by
Jason Houston for Wake Forest University.
River mining waned in the United States and other countries with 19th and early-20th century rushes. In some countries, legislation established regulations forbidding most river mining activity. Shifts to hard-rock mining in large pits or underground veins proved to be more lucrative in some instances.
However, a major river mining boom, especially targeting gold, is underway across the global tropics. That boom is the subject of this work.
